Recently, small electronic devices are widely used which devices include a module with built-in electronic components which includes a board, plural electronic components arranged on the board, and a resin mold for covering the electronic components. FIG. 17 is a sectional view of conventional module 101 with a electronic component molded with resin. Wiring board 102 has a surface having wiring pattern 111 and electrode 103 thereon, and the surface is covered with solder resist 106. Wiring board 102 has inner via 110 electrically connecting wiring pattern 112 and backside electrode 113 formed on the backside of wiring board 102. Backside electrode 113 is provided with solder 114 for connecting the electrode to a motherboard (not illustrated). Electronic component 104 and electrode 103 are connected with solder 105, and then the surface of wiring board 102 is covered with insulating resin 107 so as to wrap electronic component 104. The surface of module 101 is provided with metal-plated, electromagnetic shield layer 115 thereon.
In conventional module 101, electronic component 104 is mounted and on wiring board 102, and wired with solder and bonding wires.
The mounting with bonding wires requires a larger area than that of electronic component 104 for joining with wires, thus making the module unsuitable for reducing the size of electronic devices.
Meanwhile, The mounting with solder requires an area substantially identical to the size of the electronic component although fillet at an end of electrode 103 is needed, thus making the module suitable for reducing the size of electronic devices. However, in order to prevent short-circuit due to the solder, portions except for the electrodes on the surface of wiring board 102 are required to cover with solder resist 106. In order to prevent short-circuit between electrodes upon its mounting, a very small amount of solder is used. Therefore, clearance 107A between electronic component 104 and wiring board 102 covered with solder resist 106 after the mounting is approximately maximum 10 μm. When electronic component 104 is molded with insulating resin 107, the resin 107 does not flow into clearance 107A sufficiently, hence causing a space in the clearance.
If module 101 having the space in clearance 107A is joined to the motherboard with solder, solder 105 may melt in module 101, and the melting solder 105 flows into clearance 107A. Consequently, the solder causes short-circuiting failure between electrodes 103, hence ruining a function of module 101.
In order to fill clearance 107A between electronic component 104 and wiring board 102 with the insulating resin, the vacuum printing method is proposed. The insulating resin often contains inorganic filler, such as SiO2, having a particle diameter of several dozen micrometers. Therefore, it is difficult to fill clearance 107A of approximately 10 μm with an insulating resin even by the vacuum printing method.
Clearance 107A between electronic component 104 and photo-resist 106 may be filled with underfill having a particle diameter less than 10 μm. However, such underfill is very expensive since being made of finely-classified inorganic filler.
FIG. 18 is a sectional view of another conventional module with built-in electronic components molded with an insulating resin. Wiring board 1102 has a surface having wiring pattern 1111 thereon and electrode 1103. The surface is covered with solder resist 1116. Wiring board 1102 is provided with inner via 1110 and wiring pattern 1112 therein. Wiring board 1102 is provided with backside electrode 1113 and solder 1114 on the backside electrode. Electrode 1106 of electronic component 1104 and electrode 1103 of wiring board 1102 are connected with solder 1105, and then the surface of wiring board 1102 is covered with insulating resin 1107 so as to wrap electronic component 1104. Module 1110 has metal-plated, electromagnetic shield layer 1115 thereon.
Module 1100 is mounted on a motherboard with reflow soldering. In this case, solder 1105 in module 1100 melts and has its volume expanding. The volume expansion of solder 1105 may apply a stress to electronic component 1104, so that the stress will tear electronic component 1104 from portion 1107A of insulating resin 1107 intervening between electronic component 1104 and wiring board 1102. Consequently, solder 1105 may flow out between electronic component 1104 and insulating resin 1107, hence causing short-circuiting between electrodes 1103.
Conventional modules similar to above-mentioned ones are disclosed in Japanese Patent Laid-Open Publication Nos.2001-24312, 11-163583, and 2001-168493.